The present invention relates to waveguides for optical transmission.
Optical waveguides are generally known to provide a path for optical transmission.
Mechanically active waveguides or waveguide regions make use of movement of the transmission to create devices such as routers, evanescent switches, attenuators and the like.
Surface waveguides are typically formed using multiple silicon dioxide film layers. First, a film of low refractive index silicon dioxide is deposited on a silicon substrate to form a lower cladding layer. A second film of higher index silicon oxide is deposited on the lower cladding and then patterned to form the core region. Finally, another film of lower index silicon oxide is conformingly deposited over the core to surround the core region completely with cladding material.
However, this process creates silicon dioxide film layers that are inherently under compressive stress. This residual compressive stress leads to unstable mechanical behavior such as buckling if the waveguide is not rigidly supported by a cladding and/or substrate. This is especially true when a mechanically active waveguide is being formed and the released region exceeds a few microns in length.
Deficiencies of the prior art are overcome by the present invention which is directed to a waveguide comprising a mechanically active silicon-rich silicon nitride core in a micromechanical region. In such a waveguide the use of a silicon-rich silicon nitride core having an air cladding or a silicon-rich silicon nitride cladding in the mechanically active region is preferred.
xe2x80x9cSilicon-richxe2x80x9d silicon nitride compounds are defined as silicon nitrides having a ratio of greater than 3 silicon atoms to 4 nitrogen atoms per molecule. For example, silicon nitride compounds having the formula Si3N4 are considered stoichiometric. Silicon nitride compounds with higher silicon content are considered silicon-rich silicon nitrides.
Significantly, it has been determined herein that as the silicon content in the silicon nitrides increases, the index of refraction of the film increases and the tensile stress in the film used for the waveguide decreases. These films can be used to create membrane based micromechanical waveguide structures having a mechanically active silicon-rich silicon nitride core in the micromechanical, or movable region. The silicon-rich silicon nitride can be mechanically moved without compromising the mechanical features, unlike known waveguides using silicon oxide films which are known to have significant compressive stress.
The reduced tensile stress films of the present invention allow for the manufacture of a wide range of mechanically active waveguides which expand the possible applications of waveguides in optical transmissions.